Posted
by
Soulskill
on Thursday February 21, 2008 @06:09PM
from the ye-olde-moone dept.

The Narrative Fallacy brings news that NASA has awarded a $500,000 grant to develop plans for an array of radio telescopes to be located on the moon. The telescopes would be used to gather data from the earliest stars and galaxies, observations of which are difficult from Earth due to the ionosphere and terrestrial broadcasts. The grant was part of NASA's sponsoring of 19 "Next Generation Astronomy Missions." Quoting:
"The Lunar Array for Radio Cosmology (LARC) project ... is planned as a huge array of hundreds of telescope modules designed to pick up very-low-frequency radio emissions. The array will cover an area of up to two square kilometers; the modules would be moved into place on the lunar surface by automated vehicles. The new lunar telescopes would add greatly to the capabilities of a low-frequency radio telescope array now under construction in Western Australia, one of the most radio-quiet areas on Earth."

Like most of NASA's programs, this basically amounts to a jobs program for scientists/engineers. Notice that the funding is for the plans for an array of telescopes, not for the actual construction of said array. Building an array of telescopes on the Moon would likely require astronauts to spend months on the Moon, even if most of the telescopes came pre-assembled. Without any infrastructure on the Moon to support those astronauts, building an array of telescopes there is a pipe dream, and will remain so for the foreseeable future.

If any plans end up being actually produced, they'll likely be filed away in a drawer and forgotten. Pessimistic? Sure. But, that's the way NASA has worked for decades now.

This type of observatory requires a lot of smaller units that add up to a total resolution of the receiving surface. The best resolution is directly overhead of the site. As you try to observe items that are low on the horizon, you lose a great deal of the quality of the observation as the effective size of the array is diminished.

For example:

**** (what you are observing)

^^^^ (The array).

The array is effectively as wide as its deployment diameter.

Now, suppose you are observing from a couple other angles:

****

^^^^

From that angle, the array is apparently smaller. You can angle them to make sure you have the same strength, but you have to increase the size of the array as a direct function of the observation angle to give equivalent baselines for the observation.

So, yes, you can see in any direction around the Moon, but placement on the Moon is not a simple matter.

Consider that you don't want it pointing towards the sun either. Or, maybe you do. That's an interesting argument right there. You'll get data from the sun, but you'll also have periods where you have nothing *but* data from the sun. Similarly, Jupiter kicks out a lot of radio signals. A lot of design decisions end up still needing a fairly complex shield to make sure that you're getting only the radio waves you are searching for.

Arguably, you would want to place it near the lunar poles. Not for any of the BS arguments about the potential for water there, but because they have the least interference from Earth and the Sun. It also means you can survey the same stretch of sky for longer periods as out-of-plane bodies there are a lot easier to track and remain in the same cone of observation irrespective of the current lunar position. (ie, something that is at zenith over the lunar pole is not going to vary more than about 6 degrees from being overhead over the course of a year. Even something 25 degrees, or so, would still be visible pretty much all the time). If you go to lower latitudes, then it gets closer to a 14-day non-observation lineup followed by a 14 day period of variable observation from minimal to optimal and back as the object traverses the sky. The closer you get to the lunar equator, the more of the sky you will see, but the less the observation time and the more variable the quality of the observation.

Ideally, they design a small inexpensive setup which can be done a few times on various areas of the Moon. Just choosing one set of criteria is going to be interesting. This is not like Hubble which can be pointed in any direction. There are a lot of rocks in the way.

Logged in to post exactly this. Putting a telescope in a lagrange point solves the problem of not being able to directly communicate with it due to it being on the other side of the moon. Another advantage of direct communication is getting visual confirmation of any movements or adjustments made. Sensors are great, but I don't care how good the tech is - something will always go wrong that you didn't think of.